Rechargeable Magnesium and Sodium-ion Batteries

Lithium-ion batteries are rapidly becoming the technology of choice for the next generation of Electric Vehicles – including Hybrid, Plug-in Hybrid and Battery EVs and for grid-connected energy storage for renewable energy sources like wind and solar power. The rechargeable lithium-ion battery is the power source of choice in present-day electronic applications.

Introduced in the 1990’s, it has exhibited an annual market penetration rate of 25%, replacing nickel metal hydride batteries. It has reached a specific energy of 175 Wh/kg, and advanced polymer systems are capable of reaching 200-250 Wh/kg. However, technological barriers of higher lithium intercalation in the graphite anode and the oxide cathode, and attendant weight penalties, constrain further improvements in energy density of the current lithium-ion electrochemical system. The recent increases in the cost of Cobalt have also put heavy price pressures on present Li-ion battery manufacturers. While alternative cathode materials with higher capacity have been investigated, safety has become a prime constraint.

In addition, an analysis of Lithium's geological resource base shows that there is insufficient Lithium available in the Earth's crust to sustain Electric Vehicle manufacture or Grid-connected energy storage requirements in the volumes required, if based solely on Li-ion batteries.

Nrgtek is currently working to demonstrate a pathway for a low-cost, high energy-density and power-density rechargeable hybrid flow battery/ regenerative fuel cell system.

Magnesium is an attractive material for the negative electrode of a rechargeable battery, since it has a high electrochemical equivalence of 2.20 Ah/g (as compared to 3.86 Ah/g of Li), a considerable negative potential of 2.37 volts versus SHE (as compared to 3.1 volts versus SHE for Li), theoretical cell voltage of 3.1 volts (as compared to 3.4 volts for Li) against air electrodes, and a theoretical specific energy of 6,800 Wh/kg. Magnesium is an abundantly available element in the earth’s crust (as compared to the paucity of lithium ores in the world), and is inherently safer than lithium. While magnesium-air primary batteries exist, rechargeable magnesium batteries have not yet been commercially successful, both due to the low reversibility of the Mg electrode/electrolyte ion transfer mechanism because of the passivating oxide layer on the Mg anode, the lack of suitable high-conductivity Mg++ ion conducting electrolytes, and the need for a high-voltage cathode system.

Applications for the hybrid Flow battery/RFC system include but are not limited to: